An image forming apparatus based on an electrophotographic printing method includes a photoreceptor drum, a laser scanning unit (hereinafter referred to as LSU), a charging device, and a developing device. Among them, for example, the photoreceptor drum and the charging device are mounted as an integrated process unit on the image forming apparatus. The LSU radiates laser light to the photoreceptor drum in accordance with image information, and the charging device evenly charges a surface of the photoreceptor drum.
A lens is provided on a light path of the LSU. The lens becomes tainted by fouling such as toner and dust as printing is carried out again and again. In order to deal with this, for example, Patent Literature 1 discloses a configuration in which such fouling is removed by a cleaning member.
In Patent Literature 1, a process unit is designed to be detachable from an image forming apparatus for the purpose of replacement etc. The image forming apparatus has a mechanism for positioning the process unit in front and rear directions of the image forming apparatus when the process unit is attached to the image forming apparatus. Furthermore, in a charging device included in the process unit, particularly in a charging device utilizing corona discharge, ozone is generated due to discharge. In order to deal with this, the charging device is required to take in air for exhausting the ozone. For example, Patent Literature 2 discloses a configuration in which a duct via which air is sent to a charging device is provided.